Update README.md

Author: jkleinj

README.md

@@ -2,14 +2,16 @@
 [![release](https://img.shields.io/badge/release-v0.1-green?logo=github)](https://github.com/Fraternalilab/PDBencode)
 
 The package provides the functionality to encode given PDB structures
-into Structural Alphabet strings.
+into Structural Alphabet (SA) strings.
 
 ## Usage
 Use the script *Rscripts/pdbencode.R* in the directory containing PDB file(s):
 ```{sh}
 Rscript pdbencode.R 
 ```
 All PDB files (with extension ".pdb") in that directory will be processed.
+Each structure <ID>.pdb yields an encoded <ID>_sa.fasta file containing
+one SA sequence per chain. The format of SA sequence headers is <ID>|<chain>.
 
 #### Copyright Holders, Authors and Maintainers 
 - 2021 Jens Kleinjung (author, maintainer) jens@jkleinj.eu